In memory applications in the semiconductor industries, such as DRAM and 2D NAND, plasma etching removes silicon-containing films, such as silicon oxide or silicon nitride layers, from semiconductor substrates. For 3D NAND, etching of stacks of multiple SiO/SiN or SiO/poly-Silicon (p-Si) layers is critical. See, e.g., US 2011/0180941 to Samsung Electronics Co., Ltd. An etchant having high selectivity between the mask and layers being etched is essential. Furthermore, the etched structure should have a straight vertical profile without bowing and low line edge roughness (LER).
Traditional etch gases include octafluorocyclobutane (cC4F8), hexafluoro-1,3-butadiene (C4F6), CF4, CH2F2, CH3F, and/or CHF3. It is well known that selectivity and polymer deposition rate increase as the ratio of C:F increases (i.e., C4F6>C4F8>CF4). See, e.g., U.S. Pat. No. 6,387,287 to Hung et al. In addition, other gases, such as inert gases like Ar, Kr, or Xe, are added to the plasma where they are ionized and accelerated to the wafer surface bombarding the surface and supporting the etching process. Because they are inert gases, they do not directly participate in the chemical reactions of the etching process.
However, traditional etch chemistries may not be able to provide a feature, such as a hole or trench, having an aspect ratio higher than 20:1, which is necessary in the newer applications (e.g., 3D NAND), at least due to insufficient etch resistant polymer deposition on sidewalls during the plasma etching processes. The sidewall —CxFy— polymers, wherein x ranges from 0.01 to 1 and y ranges from 0.01 to 4, may be susceptible to etching. As a result, the etched patterns may not be vertical and the etch structures may show bowing, change in dimensions, pattern collapse and/or increased roughness.
Bowing may result from sidewall etching of the mask layer, which may often be an amorphous carbon (a-C) material. The a-C materials may be etched by oxygen radicals in the plasma which may cause increased opening of the mask and result in bow-like, or angled/curved, etch structures.
Iodine-containing compounds have been used as etching gases. For example, Chung (U.S. Pat. No. 9,460,935) discloses etching first and second etching layers under plasma generated using, among others, 1,1,2,2-tetrafluoro-1-iodo-ethane. See also Karecki et al., Plasma etching of dielectric films with novel iodofluorocarbon chemistries: iodotrifluoroethylene and 1-iodoheptafluoropropane, J. Vac. Sci. Technol. A 16, 755 (1998); JP2006/108484 to Ulvac; TWI343601 to Ulvac.
It is important to minimize bowing and to achieve high aspect ratio (i.e., up to 200:1) needed for current applications (e.g., contact etch or 3D NAND). Additionally, etching today has not been limited to selectivity to the photoresist mask. It is equally important to get high selectivity among other materials such as a-C, SiN, p-Si, SiC or other forms of SiaCbOcHdNe materials (where a>0; b, c, d and e≥0).
Thus, a need remains for etch gas compositions suitable for use in plasma etching applications which maintain selectivity and high aspect ratios for a wide range of process conditions.